The present invention relates to a flat coil element for an electric motor and to a method of manufacturing the same and, more particularly, to a flat coil element for an electric motor and a method for manufacturing the same in which a rotor of a coreless motor and a flat field winding of a electric motor are formed.
Electric motors generally comprise a stator and a rotor as is well known, and the rotor moves relative to the stator in predetermined positional relation. The torque of these electric motors is generated by an electromagnetic force between the stator and the rotor. Electric motors are classified into electric motors in which vertical magnetic flux with respect to the rotating shaft is utilized, and electric motors in which horizontal magnetic flux with respect to the rotating shaft is utilized. In both electric motors, the electromagnetic force is produced in accordance with the direction of the magnetic flux and the current direction flowing through the coil mounted to the rotor so that the rotor rotates. The electromagnetic force is generated in each part of the coil upon rotation of the rotor. The coil has active and passive parts, wherein the active part provides a large force in a tangential direction and contributes to the rotating efficiency, and the passive part provides a large force in a radial direction and does not contribute to the rotating efficiency. Various proposals have been made to improve the efficiency by improving the relation between the active part and the passive part. For example, in a printed motor coil, passive parts at the inner and outer peripheries are reduced in accordance with an involute winding and the active part is increased. Further, an armature coil in which coil elements which are formed by bending in a polygonal shape, are shifted from each other in the circumferential direction, has been proposed. In the first case, the diameter of the outer periphery of the armature coil is necessarily large. Further, the polygonal coil elements have a sunbstantially large passive part, reducing the operating efficiency. This armature coil is not suitable for 2 or 4 pole electric motors. In general, the coil element of the armayture coil preferably has a linear shape. U.S. Pat. application Ser. No. 139,275 filed on Apr. 14, 1980, now U.S. Pat. No. 4,401,907 and Patent Application No. 2,509,300 filed on Apr. 16, 1980 proopose a case in which the rotating efficiency is increased by a coil element which has an arcuate conductive band. This coil element is fabricated by alternately bending a original winding which it tightly wound inside and outside so that a wave-shaped coil element is prepared. However, this bending operation is not easily accomplished.